1. Field of the Invention
This invention relates to an apparatus for processing paper sheets, which has a switchback section that reverses a conveyance direction of paper, and to a method of processing paper sheets.
2. Description of the Related Art
Apparatuses for processing paper sheets are known, which comprise a switchback roller that holds a paper sheet in nip, rotates in the forward direction to convey the paper sheet forwards and rotates in the reverse direction to convey the paper sheet backwards, while keeping the sheet in nip. Such an apparatus is disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication 2004-175507. In the apparatus disclosed in Publication 2004-175507, a sensor provided at a specific position detects the rear end of a paper sheet moving toward a switchback section and generates a signal. The signal is a trigger signal, which stops the switchback roller upon lapse of a given time. The switchback roller is then rotated in the reverse direction. Thus, the paper sheet can be stopped and then conveyed backwards at an appropriate time before its rear end passes the nip of the switchback roller. Therefore, any paper sheet can be switched back under the same condition, regardless of its size.
In this apparatus, a trouble such as a paper jam may occur at, for example, a pickup section or a sorting section. Upon noticing the jam, the operator stops the apparatus. In this case, the paper sheets in the apparatus are stopped, and no further paper jam will take place. The operator then removes the jamming paper sheets from the apparatus. Thereafter, the operator make the apparatus operate again. As a result, the paper sheets in the apparatus, which are not jamming, are conveyed forward again.
Assume that a paper sheet stopped on the way to the switchback section is conveyed again. The sheet may be conveyed backwards before its rear end comes sufficiently close to the nip of the roller if the sensor provided at the specific position detects the rear end of the paper sheet and the switchback roller is stopped at the above-mentioned appropriate time and the switchback roller is therefore rotated in the reverse direction. In other words, a paper sheet to be switched back cannot always be stopped at the same position if is position is managed by time while it is being accelerated during conveyance. This is because some time elapses before the speed of conveying the sheet becomes constant. If the paper sheet to be switched back is stopped at an inappropriate position, it cannot be orientated to a desired direction after it is switched back. This results in another paper jam.
Assume that a paper sheet once stopped, with its rear end already having passed the sensor provided at the specific position, may be conveyed again. Then, the paper sheet is unnecessarily fed into the switchback section because the sensor generates no trigger signals for stopping the sensor. Consequently, the sheet is bent in the switchback section, inevitably causing a paper jam. In this case, the paper sheet will be out of sight because the operator cannot see the interior of the switchback section.